Verifying an md5 password against plain text?

[eluser]Cheese[/eluser]
I have a simple log in system with an sql call to check for a username and password, problem is, upon registration I set the password field to be encrypted. Now when I try and log in, the sql call does not return anything since the plain text pass on the client side does not match up against the encrypted hash in the database. Is there a function to compare text strings against hash encryptions or anything like that? Or should I be verifying the password field some other way?